The present invention relates generally to an amplifying circuit for high frequency and base-band applications. More particularly, the present invention relates to a radio frequency (RF) or microwave frequency amplification circuit for use in a receive mode and in a transmit mode.
Various wireless communication systems, such as, cellular telephones, cordless telephones, wireless modems, radios, and personal handy phone systems (PHS), require intermediate frequency (IF) amplifiers which amplify or attenuate receive IF signals (.e.g., in the receive mode) and transmit IF signals (e.g., in the transmit mode). The intermediate frequency is a frequency to which a signal wave is shifted as an intermediate step in transmission or reception. The intermediate frequency can be any frequency; in radio frequency applications, the intermediate frequency is often between 1 MHz and 1 GHz.
Generally, the IF signals are amplified or attenuated by semiconductor or integrated circuit devices. In most high frequency amplification schemes, the receive IF signal and the transmit IF signal are provided through a discrete or off-chip filter to remove spacious signals outside of a band width centered at the intermediate frequency. The discrete filter is generally a physically large device which cannot be integrated on a semiconductor substrate.
With reference to FIG. 1, a communication system 10 includes a conventional IF amplifier circuit 9 integrated on a semiconductor substrate 11. Circuit 9 includes a receive path amplifier 20, a transmit path amplifier 22, a receive path amplifier 24, a transmit path amplifier 26, a switch circuit 28, and a switch circuit 30. Switch circuit 28 includes a terminal 44, a terminal 46, and a common terminal 54. Switch circuit 30 includes a common terminal 56, a terminal 48, and a terminal 52.
Amplifier 20 has an input coupled to a receive path input 12 and an output coupled to terminal 44 of switch circuit 28. Amplifier 22 has an input coupled to terminal 46 of switch circuit 28 and an output coupled to transmit path output 18. Amplifier 26 has an input coupled to transmit path input 16 and an output coupled to terminal 52 of switch circuit 30. Amplifier 24 has an input coupled to terminal 28 of switch circuit 30 and an output coupled to receive path output 14.
An off-chip filter 38 is coupled between amplifiers 20 and 24 and between amplifiers 22 and 26 (e.g., between switch circuits 28 and 30). Filter 38 has a terminal 40 coupled to common terminal 54 of switch circuit 28 and a terminal 42 coupled to common terminal 56 of switch circuit 30.
In a receive mode of operation, receive IF signals are provided on receive path input 12 and amplified by amplifier 20. The amplified IF signal is provided through switch circuit 28, filter 38, and switch circuit 30 to amplifier 24. Amplifier 24 reamplifies the IF signal and provides the signal to receive path output 14. Receive path input 12 and receive path output 14 can be terminals, pins, or off-chip connections for substrate 11, or they can be internal connections to other circuit components on substrate 11.
In a transmit mode of operation, transmit IF signals are provided on transmit path input 16 and amplified by amplifier 26. The amplified IF signal is provided through switch circuit 30, filter 38, and switch circuit 28 to amplifier 22. Amplifier 22 reamplifies the IF signal and provides the transmit IF signal to transmit path output 18. Transmit path input 16 and transmit path output 18 can be terminals, pins, or off-chip connections for substrate 11, or they can be internal connections to other components on substrate 11.
Amplifier circuit 9 associated with system 10 and semiconductor substrate 11 is disadvantageous for various reasons. First, amplifier circuit 9 requires identical input/output (I/O) impedances for amplifiers 20, 22, 24, and 26. For example, the output impedance of amplifier 20 must match the input impedance for amplifier 22 as well as for filter 38. Similarly, the input impedance for amplifier 24 must match the output impedance for amplifier 26 as well as for filter 38. Matching amplifier I/O impedances is difficult and adds to the complexity of designing amplifier circuit 9 on substrate 11, especially in light of differing temperature characteristics and process variations associated with amplifiers 20, 22, 24, and 26. Second, amplifier circuit 9 requires that off-chip filter 38 be bidirectional. In the receive mode, the IF signal travels from terminal 40 to terminal 42. In the transmit mode, the IF signal travels from terminal 42 to terminal 40. Bidirectional filters are more expensive and rarely have exactly the same response characteristics in both directions. This scheme precludes the use of active filters. Third, the scheme for amplifier circuit 9 on substrate 11 requires that switch circuits 28 and 30 be bidirectional or passive. Bidirectional switches for high frequency circuits cannot easily be designed in bipolar silicon substrate integrated circuit devices. Switches must be carefully designed so as not to degrade impedances which may lead to excessively large or complicated circuitry.
Thus, there is a need for an IF amplifier circuit which can utilize unidirectional switches and unidirectional filters. Further, there is a need for an IF amplifier circuit which utilizes two amplifiers for both the receive mode and the transmit mode of operation. Further still, there is a need for an amplifier scheme where IF amplifier outputs do not have to be matched to IF amplifier inputs as well as to the off-chip filter.
The present invention relates to a high frequency amplification circuit integrated on a single substrate for use with an off-chip filter. The amplification circuit operates in a receive mode and in a transmit mode. The amplification circuit includes a first switch, a first amplifier, a second amplifier, and a second switch. The first switch has a receive input, a transmit input, and a common output. The first amplifier has a first input and a first output. The first input is coupled to the common output of the first switch. The first output is coupleable to the off-chip filter. The second amplifier has a second input coupleable to the off-chip filter and a second output. The second switch has a common input, a transmit output, and a receive output. The common input is coupled to the second output.
The present invention is further related to an intermediate frequency amplifier circuit for use in a receive mode and in a transmit mode. The intermediate frequency amplifier circuit includes a first intermediate frequency switch circuit, a first amplifier circuit, a second amplifier, and a second intermediate frequency switch circuit. The first intermediate frequency switch circuit has a receive input, a transmit input, and a first switch output. The first amplifier circuit has a first amplifier input and a first amplifier output. The first amplifier input is coupled to the first switch output. The second amplifier has a second amplifier input and a second amplifier output. The second amplifier input is in communication with the first amplifier output. The second intermediate frequency switch circuit has a second switch input, a transmit output, and a receive output. The second switch input is coupled to the second amplifier output. The intermediate frequency amplifier circuit has a unidirectional signal path through the first and second amplifiers for both the receive mode and the transmit mode.
The present invention still further relates to an intermediate frequency amplifier having a receive mode and a transmit mode. The intermediate frequency amplifier includes a first intermediate frequency switch means for coupling a receive input to a first switch output in the receive mode and for coupling a transmit input to the first switch output in the transmit mode, a first amplifier means for amplifying a signal on the first switch output, a second amplifier means for amplifying the amplified signal from the first amplifier means, and a second intermediate frequency switch means for coupling a receive output to the second amplifier means in the receive mode and for coupling a transmit output to the second amplifier means in the transmit mode.
In one exemplary aspect of the present invention, the receive path and the transmit path for two IF amplifier stages are the same. Attenuation or gain control circuitry can be provided with one of the two amplifier stages for gain control in both the receive mode and in the transmit mode of operation. The gain control circuitry includes a matrix of switched resistors.
In another exemplary aspect of the present invention, a first amplifier receives the signal on either the receive path input or on the transmit path input, and a second amplifier provides the amplified signal to the receive path output or to the transmit path output. An off-chip filter can be employed between the first amplifier and the second amplifier. The filter can be unidirectional and has the same filter characteristics and impedance for both the receive mode and the transmit mode. Additionally, unidirectional switches, as opposed to bidirectional switches or passive switches, can be utilized.
According to yet another aspect of the present invention, the IF amplifier circuit includes two amplifiers. The first amplifier is a totem pole amplifier, including a current mirror. The second amplifier includes a common mode transistor amplifier and a common gate transistor amplifier. The first amplifier combines differential signals into a single signal for input to an off-chip filter, and the second amplifier splits the single signal from the filter and provides a differential output signal.
In still a further aspect of the present invention, the IF amplifier circuit is preferably part of an integrated circuit in a communication device, such as, a personal handy phone system. The IF amplifier operates at a frequency of approximately 250 MHz for a system which transmits and receives RF signals at approximately 1.9 GHz. The IF amplifier circuit provides the transmit signal and the receive signal to other on-chip devices.